1. Field of the Invention
The present invention relates to an image forming apparatus, and particularly relates to an image quality adjustment technology that is applied to the image forming apparatus according to an electrophotography method.
2. Description of Related Art
In the image forming apparatus according to the electrophotography method, in order that desired image quality is obtained, control parameter values are set beforehand for each gradation of respective colors that constitute a predetermined color space (for example, the CMYK color space). On the other hand, even when the image forming apparatus is controlled by the same control parameter values, gradations change due to the influence of environmental (temperature and/or humidity, etc.) change, time-related deterioration of the apparatus and so forth, which can make it difficult for the apparatus to reproduce desired gradations.
For this reason, various technologies to correct gradations have been proposed hitherto (for example, see Japanese Patent unexamined publication No. 2004-179768 bulletin). For the correction of gradations, typically, a test pattern showing a concentration change of each color is used. Here, the concentration change is often expressed by halftone dots or dot lines. Then, so that the desired gradation is reproduced, the control parameter values are corrected based on the concentration change of each color shown in the test pattern.
However, there has been a problem that even a patch representing the same gradation of the same color in the test pattern cannot necessarily reproduce the same concentration all the time. A major cause of this includes the fact that reproducibility in state of size, concentration distribution, edge shape or the like has deteriorated in a single dot or dot line. For this reason, with the conventional technologies, it has been difficult to realize a high-precision gradation correction.